This application is based on Japanese Patent Application Nos. 11-352104 filed Dec. 10, 1999 and 2000-174029 filed Jun. 9, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a braking system for an automotive vehicle, and more particularly to improvements of a vehicle braking system.
2. Discussion of Related Art
The assignee of the present application filed Japanese Patent Application No. 11-184816 (which has not been published at the time the present invention was made), which discloses a braking system for an automotive vehicle, wherein an assisting force other than an operating force acting on a brake operating member is applied to a pressurizing piston of a master cylinder, so that the operating force of the brake operating member is boosted by the assisting force. Described more specifically, the pressurizing piston is fluid-tightly and slidably received in a housing of the master cylinder, and cooperates with the housing to define a pressurizing chamber on the front side of the pressurizing piston, and an assisting chamber on the rear side of the pressurizing piston. A pressurized working fluid is supplied into the assisting chamber, to apply an assisting force to the pressurizing piston, whereby the operating force applied to on the brake operating member is boosted by the assisting force. In this vehicle braking system, the pressure of the fluid to be delivered from the master cylinder can be controlled in relation to the brake operating force, by controlling the pressure of the fluid supplied into the assisting chamber.
In the vehicle braking system described above, the operating stroke of the brake operating member is not controlled in relation to the operating force, and the operating stroke is determined by the operating state in a portion of the braking system between the master cylinder and a wheel brake cylinder. Accordingly, the operating stroke of the brake operating member which corresponds to a given operating force may fluctuate.
It is therefore an object of the present invention to provide a braking system for an automotive vehicle, which is capable of controlling the operating stroke of the brake operating member in relation to the operating force.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking system for a vehicle having a wheel, comprising:
a master cylinder including a cylinder housing, and a pressurizing piston which is fluid-tightly and slidably received in the cylinder housing and which cooperates with the cylinder housing to define a pressurizing chamber and an assisting chamber on respective front and rear sides of the pressurizing piston;
a brake operating device including a brake operating member manually operable with a brake operating force to apply a pressurizing force based on the brake operating force to the pressurizing piston;
a brake for braking the wheel;
a wheel brake cylinder which is connected to the master cylinder, for activating the brake;
a hydraulic pressure source operable to pressurize a working fluid;
a reservoir;
a first flow control device connected to the assisting chamber, the hydraulic pressure source and the reservoir, and operable to control flows of the fluid between the assisting chamber, and the hydraulic pressure source and the reservoir; and
a second flow control device connected to the pressurizing chamber, the hydraulic pressure source and the reservoir, and operable to control flows of the fluid between the pressurizing chamber, and the hydraulic pressure source and the reservoir.
The brake operating member may be a brake pedal operable by depression by foot of an operator of the vehicle, or a in brake lever operable by hand of the vehicle operator, for instance.
In the braking system constructed according to the above mode (1) of this invention, the fluid pressure in the pressurizing chamber (hereinafter referred to as xe2x80x9cmaster cylinder pressurexe2x80x9d where appropriate) and the operating stroke of the brake operating member (hereinafter referred to as xe2x80x9cbrake operating strokexe2x80x9d where appropriate) can be controlled to suitable values determined in relation to the operating force of the brake pedal (hereinafter referred to as xe2x80x9cbrake operating forcexe2x80x9d where appropriate). When the pressurized fluid is supplied from the hydraulic pressure source to the assisting chamber of the master cylinder, the brake operating force is boosted by the fluid pressure in the assisting chamber. When the pressurized fluid is discharged from the assisting chamber to the reservoir, the volume of the assisting chamber is reduced to thereby permit a retracting movement of the pressurizing piston. Therefore, the master cylinder pressure can be controlled to a suitable value determined by the specific brake operating force, by controlling the first flow control device to control the fluid flows to and from the assisting chamber. When the pressurized fluid is supplied from the hydraulic pressure source to the pressurizing chamber, the distance of an advancing movement of the pressurizing piston required to obtain a certain value of the fluid pressure in the pressurizing chamber can be made smaller than when the pressurized fluid is not supplied to the pressurizing chamber. On the other hand, the distance of the advancing movement of the pressurizing piston is increased as the pressurized fluid is discharged from the pressurizing chamber to the reservoir. Therefore, the brake operating stroke can be controlled to a suitable value determined by the brake operating force, by controlling the second flow control device to control the fluid flows to and from the pressurizing chamber. Thus, the three parameters, that is, the brake operating force, the brake operating stroke and the master cylinder pressure can be controlled in predetermined relationships with each other, by suitably controlling the first and second flow control devices to control the fluid flows to and from the assisting chamber and the fluid flows to and from the pressurizing chamber.
The present braking system is further advantageous in that the vehicle wheel can be braked with the fluid pressure in the pressurizing chamber, without an operation of the brake operating member, by controlling the second flow control device to control the fluid flows to and from the pressurizing chamber, namely, to control the fluid pressure in the pressurizing chamber. The master cylinder may be arranged such that when the pressurizing piston is placed at its fully retracted position, the pressurizing chamber is held in communication with the reservoir, generally, through a fluid passage whose cross sectional area is comparatively small. In this arrangement, the first flow control device is preferably activated to supply the assisting chamber with a relatively small amount of the pressurized fluid received from the hydraulic pressure source, in order to advance the pressurizing piston by a distance necessary to disconnect the pressurizing chamber from the reservoir, before the pressurized fluid is supplied from the hydraulic pressure source through the second flow control device.
Further, the wheel can be braked without an operation of the brake operating member and without an operation of the second flow control device. That is, the first flow control device is activated to supply the pressurized fluid to the assisting chamber for thereby advancing the pressurizing piston to pressurize the fluid in the pressurizing chamber. However, if the vehicle operator operates the brake operating member while the wheel is braked in the above-indicated condition, the brake operating member has been displaced from the original or non-operated position, where the brake operating member is operatively connected to the pressurizing piston such that the brake operating member is moved with the pressurizing piston. Accordingly, the vehicle operator is likely to recognize the displacement of the brake operating member from the non-operated position, and feel uneasy with this displacement. Where the brake operating member is connected to the pressurizing piston such that the brake operating member is not displaced by a movement of the pressurizing piston, the, advancing movement of the pressurizing piston by the fluid pressure in the assisting chamber causes a considerable amount of play of the brake operating member, which is also likely to be felt uneasy by the vehicle operator. In this respect, the operation of the second flow control device to supply the pressurized fluid to the pressurizing chamber is more desirable than the operation of the first flow control device to supply the pressurized fluid to the assisting chamber.
The brake application to the vehicle wheel by controlling the first or second flow control device without an operation of the brake pedal as described above may be utilized as an automatic braking control for automatically activating the wheel brake to brake the vehicle when a distance between the vehicle and a vehicle running in front of the vehicle in question has become smaller than a predetermined lower limit. Alternatively, the brake application indicated above may be utilized as a traction control or a vehicle running (turning) stability control for controlling the fluid pressure in the wheel brake cylinder. Further, the present braking system can be operated in various other manners. For instance, the master cylinder can be used as a stroke simulator which will be described, when the vehicle is braked by a regenerative braking apparatus adapted to generate a regenerative braking torque.
(2) A braking system according to the above mode (1), wherein at least one of the hydraulic pressure source and the reservoir consists of a first portion and a second portion which are connected to the first and second flow control devices, and the first and second flow control devices are operable independently of each other.
A single hydraulic pressure source may be used commonly for the first and second flow control devices. Similarly, a single reservoir may be used commonly for the first and second flow control devices. In this case, the braking system can be simplified in construction and is available at a reduced cost. However, the hydraulic pressure source may consist of a first portion and a second portion which are connected to the respective first and second flow control devices. Namely, separate first and second hydraulic pressure sources may be provided for the respective first and second flow control devices. Similarly, the reservoir may consist of a first portion and a second portion which are connected to the respective first and second flow control devices. Namely, separate first and second reservoirs may be provided for the respective first and second flow control devices. The first and second flow control devices may be arranged to supply respective predetermined amounts of the pressurized fluid from the hydraulic pressure source (common hydraulic pressure source or separate first and second hydraulic pressure sources) to the assisting chamber and the pressurizing chamber, respectively. For enabling the braking system to be operated in various modes of operations, however, the first and second flow control devices are preferably arranged to be operated independently of each other, to supply the respectively controlled amounts of the pressurized fluid from the hydraulic pressure source to the assisting and pressurizing chambers, respectively.
(3) A braking system according to the above mode (1) or (2), wherein at least one of the first and second flow control devices includes a linear control valve capable of continuously changing at least one of a rate of flow and a pressure of the fluid.
The first flow control device and/or the second flow control device may include a solenoid-operated shut-off valve or directional control valve capable of controlling the fluid flows to and from the assisting chamber or the pressurizing chamber. However, at least one of the first and second flow control devices preferably includes a linear control valve capable of controlling at least one of a fluid flow to the assisting or pressurizing chamber and a fluid flow from the assisting or pressurizing chamber, for improving the accuracy of control of the fluid flows.
(4) A braking system according to any one of the above modes (1)-(3), wherein at least one of the first and second flow control devices includes a supply-flow control valve device for controlling a flow of the fluid to a corresponding one of the assisting and pressurizing chambers, and a discharge-flow control valve device for controlling a flow of the fluid from the corresponding assisting or pressurizing chambers.
In the braking system according to the above mode (4) wherein at least one of the first and second flow control device includes both the supply-flow control valve and the discharge-flow control valve, the fluid flows to and from the assisting chamber and/or the pressurizing chamber can be controlled with a higher degree of accuracy.
(5) A braking system according to any one of the above modes (1)-(4), further comprising a main control device for controlling the first flow control device and the second flow control device, and wherein the main control device includes a brake characteristic control portion for controlling the first and second flow control devices, so as to maintain predetermined relationships among the brake operating force and an operating stroke of the brake operating member and an operating state of the wheel brake cylinder.
The xe2x80x9coperating statexe2x80x9d of the wheel brake cylinder may be obtained from or represented by, for example, a pressure of the fluid in the wheel brake cylinder, or a braking force generated by the wheel brake cylinder, more specifically, a force by which a friction member such as a brake pad or she is forced against a rotary member such as a disc rotor or a brake drum rotating with the wheel, by the wheel brake cylinder activated by the pressurized fluid. Alternatively, the operating state of the wheel brake cylinder may be obtained from or represented by a braking effect provided by the brake, for instance, by a braking torque applied to the wheel or a deceleration value of the vehicle braked by the brake.
The brake characteristic control portion of the main control device may be arranged to control the first and second flow control devices such that two of the operating force and stroke of the brake operating member and the operating state of the wheel brake cylinder are controlled in respective predetermined relationships with the other of the operating force and stroke of the brake operating member and the operating state of the wheel brake cylinder, for instance, such that the operating state of the wheel brake cylinder and the operating stroke of the brake operating member are controlled in respective predetermined relationships with the operating force of the brake operating member, or such that the operating state of the wheel brake cylinder is controlled in a predetermined relationship with the operating force of the brake operating member, and the operating stroke of the brake operating member is then controlled in a predetermined relationship with the operating state of the wheel brake cylinder.
By controlling the three parameters consisting of the operating force and stroke of the brake operating member and the operating state of the wheel brake cylinder in respective predetermined relationships with each other as described above, it is possible to prevent the brake from producing a braking force which is excessively large with respect to the specific operating force of the brake operating member, or prevent the operating stroke of the brake operating member which is excessively large with respect to the operating force. Accordingly, the present arrangement is effective to improve the operating feel of the brake operating member as sensed by the vehicle operator.
(6) A braking system according to any one of the above modes (1)-(5), further comprising:
a regenerative braking apparatus including an energy converting device operable to convert a kinetic energy of the vehicle during running of the vehicle into another form of energy, and an energy storing device for storing thee above-indicated another form of energy; and
a main control device for controlling the first and second flow control devices, the main control device including a cooperative braking control portion operable to control the first flow control device such that a pressure of the fluid in the assisting chamber is lower when the regenerative braking apparatus is in operation than when the regenerative braking apparatus is not in operation.
The braking system according to the above mode (6) includes the regenerative braking apparatus, and a hydraulic braking apparatus including as major elements the master cylinder, the brake, the wheel brake cylinder, the second hydraulic pressure source and the first and second flow control devices, which have been described. In this braking system, the wheel is braked by at least one of the hydraulic braking apparatus and the regenerative braking apparatus, that is, by an operation of the brake operated by activation of the wheel brake cylinder with the pressurized fluid, and/or an operation of the regenerative braking apparatus. When the regenerative braking apparatus is operated, the first flow control valve is preferably controlled to control the fluid pressure in the assisting chamber such that the operating force of the brake or the braking effect provided by the brake is lower than that while the regenerative braking apparatus is not in operation, by an amount corresponding to the regenerative braking force or effect. However, it is not essential to control the first flow control device such that the fluid pressure in the assisting chamber during operation of the regenerative braking apparatus is controlled to be lower than that while the regenerative braking apparatus is not in operation, by the amount corresponding to the regenerative braking effect. That is, the principle of the present invention simply requires that the fluid pressure in the assisting chamber be lower while the regenerative braking apparatus is in operation than while the regenerative braking apparatus is not in operation.
(7) A braking system according to the above mode (6), further comprising:
a shutting-off valve having a closed state for disconnecting the pressurizing chamber and the wheel brake cylinder; and
a main controller for controlling the first and second flow control devices, the main controller including a stroke simulation control portion operable, when the regenerative braking apparatus is capable of generating a regenerative braking effect corresponding to an operating amount of the brake operating member, for placing the shut-off valve in the closed state, and controlling the first and second flow control devices such that the brake operating force and an operating stroke of the brake operating member while the regenerative braking apparatus is in operation are controlled to have a same relationship with each other as while the regenerative braking apparatus is not in operation.
The operating amount of the brake operating member may be the operating force or stroke of the brake operating member.
In the braking system according to the above mode (7), the operating force and stroke of the brake operating member while the regenerative braking apparatus is in operation can be controlled to have the same relationship with each other as while the generative braking apparatus is not in operation, even under the operating condition of the braking system in which the supply of the pressurized fluid from the pressurizing chamber to the wheel brake cylinder is prevented by the shutting-off valve placed in the closed state. That is, the first and second flow control devices are controlled to control the fluid flows to and from the assisting chamber and the pressurizing chamber while the pressurized fluid is discharged to the reservoir from the pressurizing chamber which is disconnected from the wheel brake cylinder by the shutting-off valve. Thus, the master cylinder is used as a stroke simulator capable of permitting the operating stroke of the brake operating member to change in a predetermined relationship with the operating force, even while the regenerative braking apparatus is in operation. The present braking system doe not require an exclusive stroke simulator, and can be simplified in construction.
(8) A braking system according to the above mode (7), wherein the main controller controls the first flow control device to control the fluid pressure in the assisting chamber to an atmospheric level and controls the second flow control device to permit the pressurized fluid to be discharged from the pressurizing chamber, when the operating amount of the brake operating member is increased while the regenerative braking apparatus is operated to generate the regenerative braking effect corresponding to the operating amount of the brake operating member.
When the vehicle is braked by only the regenerative braking apparatus, it is not required to supply a pressurized fluid to the pressurizing chamber of the master cylinder to activate the wheel brake cylinder for operating the brake. In this case, the first flow control device is controlled to control the fluid pressure in the assisting chamber to the atmospheric level, and the second flow control device is controlled control the fluid pressure in the pressurizing chamber such that the controlled fluid pressure corresponds to the operating amount of the brake operating member. This arrangement improves the operating feel of the brake operating member, since the operating force corresponds to the operating amount.
(9) A braking system according to the above mode (7) or (8), wherein the main controller controls the first flow control device to control the fluid pressure in the assisting chamber to an atmospheric level and controls the second flow control device to permit the pressurized fluid to be supplied to the pressurizing chamber, when the operating amount of the brake operating member is reduced while the regenerative braking apparatus is operated to generate the regenerative braking effect corresponding to the operating amount of the brake operating member.
Since the second flow control device permits the supply of the pressurized fluid to the pressurizing chamber, the operating amount of the brake operating member can be reduced, even while the pressurizing chamber is disconnected from the wheel brake cylinder by the shutting-off valve.
(10) A braking system according to any one of the above modes (1)-(9), wherein the cylinder housing has a cylinder bore having a small-diameter portion and a large-diameter portion having a larger diameter than the small-diameter portion, and the pressurizing piston includes a small-diameter portion engaging the small-diameter portion of the cylinder bore, and a large-diameter portion engaging the large-diameter portion of the cylinder bore, the small-diameter portion of the pressurizing piston cooperating with the cylinder housing to define the pressurizing chamber on a front side of the small-diameter portion of the pressurizing piston, while the large-diameter portion of the pressurizing piston cooperating with the cylinder housing to define the assisting chamber on a rear side of the large-diameter portion of the pressurizing piston, the small-diameter and large-diameter portions of the pressurizing piston defining a first shoulder surface, while the small-diameter and large-diameter portions of the cylinder bore defining a second shoulder surface, the cylinder housing and the pressurizing piston cooperating to define an annular chamber between the first and second shoulder surfaces, the braking system further comprising:
means for defining a connecting passage connecting the annular chamber and the pressurizing chamber; and
a check valve provided in the connecting passage, the check valve permitting a flow of the fluid in a first direction from the annular chamber toward the pressurizing chamber and inhibiting a flow of the fluid in a second direction opposite to the first direction.
In the braking system constructed according to the above mode (10) of the present invention, the pressurized fluid can flow from the annular chamber to the pressurizing chamber through the connecting passage when the brake operating member is operated. This arrangement makes it possible to increase the fluid pressure in the pressurizing chamber at a higher rate than when the fluid pressure in the pressurizing chamber is increased by an advancing movement of the pressurizing piston based on an operation of the brake operating member and by a flow of the pressurized fluid to the pressurizing chamber through the second flow control device. The present arrangement is effective to reduce a delayed increase in the fluid pressure in the pressurizing chamber of the master cylinder due to a delayed response of the second flow control device, and an accordingly delayed activation of the wheel brake cylinder, when the brake operating member is operated abruptly or at a relatively high speed, for instance.
(11) A braking system according to any one of the above modes (1)-(10), wherein the master cylinder includes a communication control device for effecting fluid communication between the pressurizing chamber and the reservoir when the pressurizing piston is placed at a fully retracted position, and inhibiting at least a flow of the fluid from the pressurizing chamber toward the reservoir when the pressurizing piston has been advanced by more than a predetermined distance, the braking system further comprising:
a main controller for controlling the first and second flow control devices, the main controller including an unintended braking control portion operable when the brake operating member is not in operation, to control the first flow control device to control the fluid pressure in the assisting chamber for advancing the pressurizing piston to be advanced by more than the predetermined distance, and control the second flow control device to increase the fluid pressure in the pressurizing chamber.
The communication control device may include portions of the cylinder housing and the pressurizing piston through which respective ports are formed such that these ports communicate with each other when the brake operating member is placed at the fully retracted position and are spaced apart from each other when the brake operating member has been advanced by more than the predetermined distance. Alternatively, the communication control device may be constituted by a shut-off valve which is mechanically opened and closed depending upon a position of the pressurizing piston.
When the brake operating member is operated, the pressurizing piston is advanced from its fully retracted position with the pressurizing force based on the operating force of the brake operating member, by more than the predetermined distance, so that the fluid in the pressurizing chamber is pressurized while the communication control device prevents a flow of the fluid from the pressurizing chamber to the reservoir. In the braking system according to the above mode (11), the first flow control device can be controlled to control the fluid pressure in the assisting chamber for advancing the pressurizing piston by more than the predetermined distance, even when the brake operating member is not in operation, so that the pressurized fluid is prevented from being discharged from the pressurizing chamber to the reservoir. Accordingly, the fluid in the pressurizing chamber can be pressurized if the second flow control device is so controlled while the brake operating member is not in operation. In this condition, too, the operating force and stroke of the brake operating member and the operating state of the wheel brake cylinder are controlled so as to satisfy the predetermined relationships with each other, by controlling the first and second flow control device. Namely, these flow control devices are controlled while the brake operating member is not in operation, to perform various braking controls as needed, for instance, a traction control, a vehicle running or turning stability control, and other automatic braking controls. In the present braking system, the pressurizing piston is advanced from its fully retracted position by more than the predetermined distance, for inhibiting the fluid flow from the pressurizing chamber to the reservoir. However, this advancing distance of the pressurizing piston is very small, so that the amount of displacement of the brake operating member caused by the advancing movement of the pressurizing piston is accordingly small, where the brake operating member is operatively connected to the pressurizing piston such that the brake operating member is displaced with a movement of the pressurizing piston. Where the brake operating member is operatively connected to the pressurizing piston such that the brake operating member is not displaced with the pressurizing piston, the amount of play of the brake operating member after the pressurizing piston has been advanced by more than the predetermined distance is also small since the predetermined distance of the advancing movement of the pressurizing piston is very small. Accordingly, the vehicle operator is unlikely or less likely to feel a displacement of the brake operating member or an excessive amount of play of the brake operating member, when the brake operating member is operated during any automatic braking control.
(12) A braking system according to the above mode (11), further comprising a wheel-brake-cylinder-pressure control device disposed between the pressurizing chamber, and the wheel brake cylinder and a reservoir device, the wheel-brake-cylinder-pressure control device being operable to control a pressure of the fluid in the wheel brake cylinder, and wherein the unintended braking control portion controls the second flow control device to increase a pressure of the fluid in the pressurizing chamber to a level high enough to permit the pressurized fluid in the pressurizing chamber to be used as a hydraulic pressure source for the wheel-brake-cylinder-pressure control device.
The fluid pressure in the wheel brake cylinder can be controlled by controlling the second flow control device to control the fluid pressure in the pressurizing chamber. In the braking system according to the above mode (12) wherein the wheel-brake-cylinder-pressure control device is provided, the fluid pressure in the wheel brake cylinder can be controlled to a value different from the value of the fluid pressure in the pressurizing chamber. Where the braking system includes wheel brake cylinders for braking a plurality of wheels, the fluid pressure in the different wheel brake cylinders can be controlled to respective different values. Therefore, the present arrangement permits improved accuracy of control of the fluid pressure in the wheel brake cylinder, in the traction control or any other automatic braking control, which is effected while the brake operating member is not in operation.
(13) A braking system according to any one of the above modes (1)-(12), wherein the first flow control device includes a pilot-operated pressure regulator operable to control the pressure of the pressurized fluid received from the hydraulic pressure source, to a value corresponding the pressure of the fluid in the pressurizing chamber received as a pilot pressure.
The pilot-operated pressure regulator provided in the braking system according to the above mode (13) is operated when the first flow control device fails to normally operate to control the flows of the fluid to and from the assisting chamber, due to a defect of the hydraulic pressure source, for example. The pressure regulator is arranged to control the pressure of the pressurized fluid received from the hydraulic pressure source, to a value corresponding to the fluid pressure in the pressurizing chamber, and apply the controlled fluid pressure to the assisting chamber, so that the operating force of the brake operating member is boosted by the fluid pressure in the assisting chamber.
(14) A braking system according to the above mode (13), wherein the first flow control device comprises:
an electrically operated hydraulic pressure control device disposed in parallel connection with the pilot-operated pressure regulator and electrically controlled to control the pressure of the fluid in the assisting chamber; and
a selecting device connected to the pilot-operated pressure regulator, the electrically operated hydraulic pressure control device and the assisting chamber, and operable to selectively apply to the assisting chamber the fluid pressure controlled by the pilot-operated pressure regulator or the electrically operated hydraulic pressure control device.
In the braking system according to the above mode (13), one of the fluid pressures controlled by the pilot-operated pressure regulator and the electrically operated hydraulic control device is selectively applied to the assisting chamber, so that the operating force of the brake operating member can be boosted by the fluid pressure in the assisting chamber even when the fluid pressure controlled by the electrically operated hydraulic pressure control device cannot be applied to the assisting chamber, for example, since the fluid pressure regulated by the pilot-operated pressure regulator is applied to the assisting chamber.
(15) A braking system according to the above mode (14), wherein the selecting device includes a change valve operable to apply to the assisting chamber a higher one of the fluid pressures controlled by the pilot-operated pressure regulator and the electrically operated hydraulic pressure control device.
(16) A braking system according to the above mode (14), wherein the selecting device includes a shutting-off device connected between the pilot-operated pressure regulator and the assisting chamber and operable to disconnect the pilot-operated pressure regulator and the assisting chamber from each other.
The shutting-off device may be a solenoid-operated shut-off valve.
(17) A braking system according to the above mode (13), wherein the pilot-operated pressure regulator has a high-pressure port connected to the hydraulic pressure source, a control-pressure port connected to the assisting chamber, a low-pressure port connected to the reservoir, and a pilot-pressure port connected to the pressurizing chamber, the pressure regulator being operable to effect fluid communication of the control-pressure port with the high-pressure port or the low-pressure port, for increasing or reducing the fluid pressure in the control-pressure port, depending upon the fluid pressure applied to the pilot-pressure port.
The pilot-operated pressure regulator is adapted to control the fluid pressure in the control-pressure port, to a value corresponding to the fluid pressure applied to the pilot-pressure port, and apply the thus controlled fluid pressure to the assisting chamber.
(18) A braking system according to the above mode (17), wherein the first flow control device includes a normally open solenoid-operated control valve connected between the low-pressure-port of the pressure regulator and the reservoir.
While the normally open solenoid-operated control valve is normally functioning, this control valve reduces the fluid pressure in the control-pressure port and therefore the fluid pressure in the assisting chamber, to a value corresponding to the operating force of the brake operating member, so that the fluid pressure in the assisting chamber is controlled so as to control the fluid pressure in the pressurizing chamber to a value which has a predetermined relationship with the operating force of the brake operating member. Further, by holding the normally open solenoid-operated control valve in the closed state while this control valve is normally functioning, the fluid pressure in the assisting chamber is prevented from being discharged to the reservoir through the control-pressure port and the low-pressure port. Accordingly, the fluid pressure received from the first flow control device rather than the fluid pressure received from the pressure regulator can be applied to the assisting chamber, so that the fluid pressure in the assisting chamber can be increased by the fluid pressure controlled by the first flow control device. Where the normally open solenoid-operated control valve cannot be closed and held open due to some defect or abnormality associated with this control valve, the fluid pressure in the assisting chamber (fluid pressure in the control-pressure port) is mechanically reduced according to the fluid pressure applied to the pilot-pressure port (according to the fluid pressure in the pressurizing chamber). The above-indicated defect or abnormality may be a failure to apply an electric current to the coil of the solenoid-operated control valve, a defect of the control valve per se, such as a failure of the control valve to normally function even with an electric current being applied to its coil, or a defect of a control device provided to control the solenoid-operated control valve.
(19) A braking system according to the above mode (18), wherein the normally open solenoid-operated control valve is a linear control valve capable of continuously controlling at least one of a flow rate and a pressure of the fluid.
(20) A braking system according to the above mode (19), further comprising a valve control device for controlling the linear control valve such that the fluid pressure in the low-pressure port is higher than the fluid pressure in the pilot-pressure port.
By controlling the fluid pressure in the low-pressure port to a value higher than the fluid pressure in the pilot-pressure port, the fluid pressure in the control-pressure port can also be controlled to a value higher than the fluid pressure in the pilot-pressure port. That is, the fluid pressure in the control-pressure port is not controlled to a value corresponding the fluid pressure in the pilot-pressure port, but is controlled by the linear control valve. Thus, the fluid pressure in the assisting chamber is controlled by the linear control valve, as if the pilot-operated pressure regulator were not provided.
(21) A braking system according to any one of the above modes (17)-(20), wherein the first flow control device includes a normally closed solenoid-operated control valve connected between the hydraulic pressure source and the assisting chamber, in parallel connection with the pilot-operated pressure regulator.
(22) A braking system according to the above mode (21), wherein the normally closed solenoid-operated control valve is a linear control valve capable of continuously controlling at least one of a flow rate and a pressure of the fluid.
(23) A braking system according to the above mode (21) or (22), further comprising a valve control device operable while the normally closed solenoid-operated control valve is normally functioning, for holding the normally closed solenoid-operated control valve in a closed state, irrespective of the fluid pressures in the pilot-pressure port and the control-pressure port.
While the normally closed solenoid-operated control valve is normally functioning, the fluid pressure of the hydraulic pressure source as controlled by this solenoid-operated control valve is applied to the assisting chamber, so that the fluid pressures in the control-pressure chamber and the pilot-pressure chamber are increased. By holding the normally open solenoid-operated control valve in the closed state, irrespective of the fluid pressures in those control-pressure and pilot-pressure chambers, however, the control-pressure port is disconnected from the reservoir and the hydraulic pressure source, so that the fluid pressure in the assisting chamber is increased by the normally closed solenoid-operated control valve, as if the pilot-operated pressure regulator were not provided. The valve control device may be adapted to control the normally closed solenoid-operated control valve such that the fluid pressure in the control-pressure port is higher than the fluid pressure in the pilot-pressure port. In this case, the control-pressure port is stably prevented from communicating with the hydraulic pressure source through the high-pressure port, so that the pressure regulator is held in a state in which it does not function, as if it were not provided. When it becomes necessary to reduce the fluid pressure in the assisting chamber, the fluid pressure in the assisting chamber is reduced by the normally open solenoid-operated control valve indicated above. In this case, the pressure regulator is preferably held in the state in which it does not function, except permitting the fluid to flow therethrough, as if it were not provided, as in the braking system according to the above mode (20).
Where the normally closed solenoid-operated control valve cannot be opened and is held closed due to a defect or abnormality associated with the control valve, the fluid pressure in the control-pressure port is mechanically increased according to the fluid pressure applied to the pilot-pressure port. In this event, the normally open solenoid-operated control valve indicated above is held in its fully open state, so s to permit the pilot-operated pressure regulator to perform its normal operation. Where the normally closed and normally open solenoid-operated control valves are both inoperable to perform their functions due to a defect of the electric system of the braking system, for example, these two control valves are both necessarily placed in the fully open state.
(24) A braking system according to any one of the above modes (17)-(23), wherein the pilot-operated pressure regulator comprises:
a control piston which receives the fluid pressure applied to the pilot-pressure port in an advancing direction thereof:
a first valve portion operable depending upon a movement of the control piston in the advancing direction or a retracting direction opposite to the advancing direction, for selectively permitting and inhibiting fluid communication between the control-pressure port and the high-pressure port; and
a second valve portion operable according to the movement of the control piston in the advancing direction or retracting direction, for selectively permitting and inhibiting fluid communication -between the control-pressure port and the low-pressure port.
(25) A braking system according to any one of the above modes (1)-(24), wherein the first flow control device comprises:
an electrically operated hydraulic pressure control device disposed between the hydraulic pressure source and the reservoir, and the assisting chamber, and electrically controlled to control the fluid pressure in the assisting chamber;
a by-pass passage which by-passes the electrically operated hydraulic pressure control device; and
a check valve device disposed in the by-pass passage, the check valve device permitting a flow of the fluid in a first direction from the reservoir toward the assisting chamber and inhibiting a flow of the fluid in a second direction opposite to the first direction.
In the braking system according to the above mode (25), the fluid can be supplied from the reservoir to the assisting chamber through the by-pass passage and the check valve device, permitting the pressurizing piston to be advanced, even where the first flow control device is defective and is not capable of supplying the assisting chamber with the pressurized fluid. Thus, the brake operating member can be operated even while the first flow control device is defective. When the brake operating member is operated abruptly or at a considerably high speed, the first flow control device may suffer from a delayed supply of the pressurized fluid to the assisting chamber. In this case, the fluid is supplied from the reservoir to the assisting chamber through the by-pass passage and the check valve device, thereby permitting the brake operating member to be operated while preventing the assisting chamber from be evacuated.
(26) A braking system according to any one of the above modes (1)-(25), wherein the second flow control device comprises:
an electrically operated hydraulic pressure control device disposed between the hydraulic pressure source and the reservoir, and the pressurizing chamber, and electrically controlled to control the fluid pressure in the pressurizing chamber; and
shutting-off device disposed between the electrically operated hydraulic pressure control device and the pressurizing chamber, for inhibiting fluid communication between the electrically operated hydraulic pressure control device and the pressurizing chamber.
The shutting-off device indicated above may be a solenoid-operated shut-off valve.
In the braking system according to the above mode (26), the fluid communication between the electrically operated hydraulic pressure control device and the pressurizing chamber can be inhibited or prevented by the shutting-off device, to inhibit or prevent fluid communication of the pressurizing chamber with the reservoir and the hydraulic pressure source through the electrically operated hydraulic pressure control device, even when the electrically operated hydraulic pressure control device of the second flow control device is not normally operable to perform its pressure control function, causing the pressurized fluid to be continuously supplied from the hydraulic pressure source to the pressurizing chamber irrespective of an operation of the brake operating member, or causing the pressurized fluid to be continuously discharged from the pressurizing chamber to the reservoir. Accordingly, the fluid in the pressurizing chamber can be pressurized to active the wheel brake cylinder by an operation of the brake operating member, even where the electrically operated hydraulic pressure control device is not normally operable.
(27) A braking system for a vehicle having a wheel, comprising:
a master cylinder including a cylinder housing, and a pressurizing piston which is fluid-tightly and slidably received in the cylinder housing and which cooperates with the cylinder housing to define a pressurizing chamber in front of the pressurizing piston, a working fluid in the pressurizing chamber being pressurized by an advancing movement of the pressurizing piston;
a brake for braking the wheel;
a wheel brake cylinder connected to the pressurizing chamber of the master cylinder, and operable with the pressurized fluid supplied from the pressurizing chamber, for activating the brake;
a brake operating device including a brake operating member manually operable with a brake operating force to apply a first pressurizing force based on the brake operating force to the pressurizing piston;
an electrically operated hydraulic pressure source operable to pressurize the working fluid and control a pressure of the pressurized fluid;
an assisting device operable to apply a second pressurizing force based on the pressurized fluid supplied from the electrically operated hydraulic pressure source; and
a pressurized-fluid supplying device for supplying the fluid pressurized by the electrically operated hydraulic pressure source to at least one of the pressurizing chamber and the wheel brake cylinder.
In the vehicle braking system according to the above mode (27), the fluid pressurized by the electrically operated hydraulic pressure source is supplied to the assisting device and to at least one of the pressurizing chamber and the wheel brake cylinder. The required operating stroke of the brake operating member is required by an amount corresponding to the pressure of the pressurized fluid supplied to the pressurizing or the wheel brake cylinder. Further, the operating stroke of the brake operating member can be controlled as desired, by controlling the amount of the pressurized fluid to be supplied to at least one of the pressurizing chamber and the wheel brake cylinder.
The pressurizing chamber may be connected through a main fluid passage to the wheel brake cylinder. A suitable pressure-increasing device or other pressure control device may be provided in the main fluid passage so that the fluid pressure in the wheel brake cylinder is controlled by the pressure control device according to the pressure of the pressurized fluid supplied from the pressurizing chamber.
The pressurized-fluid supply device may be adapted to supply the pressurized fluid from the electrically operated hydraulic pressure source to the pressurizing chamber or to the main fluid passage which connects the pressurizing chamber and the wheel brake cylinder. In the later case, the main fluid passage may be provided with a shutting-off device having a closed state and an open state for inhibiting and permitting fluid communication between the pressurizing chamber and the wheel brake cylinder. In this case, the pressurized fluid can be supplied from the pressurizing chamber to the wheel brake cylinder through the shutting-off device placed in the open state.
The assisting device may have the assisting chamber provided in the master cylinder used in the braking system according to the above mode (1). Alternatively, the assisting device may include a hydraulic cylinder separate from the master cylinder, and a force transmitting device for transmitting a force from the hydraulic cylinder to the pressurizing piston.
The electrically operated hydraulic pressure source may include the hydraulic pressure source and the first flow control device, which are provided in the braking system according to the above mode (1). The second flow control device provided in the braking system according to the above mode (1). may be considered to be an example of the pressurized-fluid supplying device in the present braking system according to the above mode (27). Alternatively, the second flow control device may be considered to be a part of the electrically operated hydraulic pressure-source, and a connecting passage connecting the second flow control device and at least one of the pressurizing chamber and the wheel brake cylinder may be considered to be the pressurized-fluid supplying device.
Thus, the vehicle braking system according to the above mode (27) may be considered to be one form of the vehicle braking system according to the above mode (1). It will be understood that the vehicle braking system according to the present mode (27 may incorporate any one of the features of the braking systems according to the above modes (2)-(24).
(28) A braking system according to the above mode (27), wherein the pressurized-fluid supplying device includes a device capable of controlling an amount of the pressurized fluid to be supplied from the electrically operated hydraulic pressure source to at least one of the pressurizing chamber and the wheel brake cylinder.
In the braking system according to the above mode (28) wherein the amount of supply of the pressurized fluid from the electrically operated hydraulic pressure source is controlled by the pressurized-fluid supplying device, the operating force of the brake operating member can be controlled in a predetermined relationship with the operating stroke of the brake operating member or the fluid pressure in the pressurizing chamber.